Flame resistant materials and method of making same

ABSTRACT

PROCESS FOR FLAMEPROOFING MATERIALS, MORE PARTICULARLY COTTON TEXTILE FABRICS, COMPRISING IMPREGNATING THE MATERIAL WITH A PHOSPHORUS COMPOUND, SUCH AS TRIALLYL PHOSPHATE, AND A COMONOMER, SUCH AS N-METHYLOL ACRYLAMIDE, AND THEREAFTER EXPOSING THE MATERIAL TO IIONIZING RADIATION AT A DOSE LEVEL TO CAUSE PRODUCTION OF A SOLID COPOLYMER OF THE PHOSPHORUS COMPOUND AND THE COMONOMER IN SITU IN THE MATERIAL. THE PREFERRED TRIALLYL PHOSPHATE AND N-METHYLOL ACRYLAMIDE ARE PRESENT IN THE IMPREGNATING BATH IN A RATIO AND CONCENTRATION SUCH THAT FLAME RESISTANCE IMPARTED TO THE MATERIAL IS RETAINED THROUGH AT LEAST FIFTEEN LAUNDERINGS UNDER STANDARDIZED CONDITIONS. THE FLAMEPROOFED MATERIALS PREPARED BY THE PROCESS, WHICH ARE DURABLE AGAINST AT LEAST FIFTEEN LAUNDERINGS, ARE DISCLOSED.

United States Patent OifiC 3,592,683 Patented July 13, 1971 3,592,683FLAME RESISTANT MATERIALS AND METHOD OF MAKING SAME Thomas D. Miles,North Randolph, Mass., and Armando C. Delasanta, Woonsocket, R.I.,assignors to the United States of America as represented by theSecretary of the Army No Drawing. Filed Sept. 25, 1969, Ser. No. 861,163Int. Cl. B4411 5/00; D06m 13/26, 15/16 US. Cl. 117-9331 10 ClaimsABSTRACT OF THE DISCLOSURE Process for flameproofing materials, moreparticularly cotton textile fabrics, comprising impregnating thematerial with a phosphorus compound, such as triallyl phosphate, and acomonomer, such as N-methylol acrylamide, and thereafter exposing thematerial to ionizing radiation at a dose level sufficient to causeproduction of a solid copolymer of the phosphorus compound and thecomonomer in situ in the material. The preferred triallyl phosphate andN-methylol acrylamide are present in the impregnating bath in a ratioand concentration such that flame resistance imparted to the material isretained through at least fifteen launderings under standardizedconditions. The flameproofed materials prepared by the process, whichare durable against at least fifteen launderings, are disclosed.

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto us of any royalty thereon.

This invention relates to a process for flameproofing inflammablematerials, such as cellulosic yarns and fabrics. More particularly, theinvention relates to a process for making inflammable materials durablyflameproof so that they will retain the flameproofness developed thereinafter numerous launderings.

In recent years many phosphorus-containing compounds have been found tobe useful as flame retardants or flameproofing agents for various typesof materials which are normally inflammable in the absence of aflameproofing agent or treatment. Among the more promising of thesephosphorus-containing flameproofing agents have been the halogenatedalkylene phosphates, especially certain brominated alkylene phosphatesand polymers thereof. However, not all alkylene phosphates are effectivefor flameproofing. For example, triallyl phosphate not only is not aflame retardant for cellulosic materials; but, when present on suchmaterials, actually increases their flammability. Polymerized triallylphosphate has flame retardant properties; but polymerization thereofheretofore has required such drastic conditions as to render theapplication of triallyl phosphate to cellulosic materials and thepolymerization thereon impractical because of resulting damage to thecellulosic material by the severe polymerization conditions heretoforefound necessary.

It is, therefore, an object of the present invention to provide a methodfor accomplishing the flameproofing of materials which are normallyinflammable by impregnating or otherwise incorporating in the material aphosphorus compound, such as triallyl phosphate, along with a comonomerand thereafter causing the phopshorus compound to copolymerize with thecomonomer in situ in the material under conditions which do notseriously harm the tensile and other physical properties of thematerial.

Another object is to flameproof cellulosic materials by polymerizingtriallyl phosphate with a comonomer absorbed therein under the influenceof relatively low doses of ionizing radiation.

A further object is to provide a practical method for flameproofingcellulosic fabrics with triallyl phosphate at sufliciently low doses ofionizing radiation to obtain a high degree of polymerization of thetriallyl phosphate in situ in the fabric without harming the physicalproperties of the fabric while markedly improving it from the standpointof flameproofness and durability with respect to laundering.

Other objects and advantages will appear from the following descriptionof the invention, and the novel features will be particularly pointedout hereinafter in connection with the appended claims.

The method of the invention is carried out by impregnating or otherwiseincorporating in an inflammable material a polymerizable phosphoruscompound, such as triallyl phosphate,and a comonomer, such as N-methylolacrylamide, and subjecting the material to high energy ionizingradiation at a dose of a level such that copolymerization occurs betweenthe phosphorus compound and the comonomer forming a copolymer of thephopshorus compound and the comonomer in situ in the material, but at alevel low enough so that relatively little or no reduction in the tearstrength and other physical properties of the material occurs as aresult of the exposure thereof to the ionizing radiation.

The preferred polymerizable phosphorus compound for use in accordancewith the present invention is triallyl phosphate. However, otherpolymerizable phosphorus compounds, such as diallyl phosphate, monoallylphosphate, or dimethyl hydrogen phosphite may be used.

The comonomers which have been found to be particularly effective withtriallyl phosphate in the production of copolymers thereof for impartingflameproofness to cellulosic and other normally inflammable materials inaccordance with this invention are N-methylol acrylamide, acrylamide,acrylic acid, and acrylonitrile. These materials may all be consideredstructurally closely related in possessing terminal double-bondedunsaturation. They are either acrylic acid or derivatives or precursorsthereof.

The low dose level of ionizing radiation employed in accomplishingcopolymerization of the triallyl phosphate with the selected comonomeris preferably about 2 megarads, but conveniently may be up to 6 megaradsor even higher, but to avoid excessive damage to the fabric or othermaterial, should be no higher than about 25 megarads. Such doses ofionizing radiation may be applied to the material from any convenientsource of ionizing radiation, such a 60 Co source or a linear electronaccelerator. In general, it is preferred to employ a linear electronaccelerator as a source of the ionizing radiation since this type ofequipment can be made to produce a high dose rate, thus making possiblea given dose over a shorter period of time with less exposure of thematerial to ionizing radiation while it is exposed to an oxygenatmosphere. Also, the shorter times required for the irradiation in alinear electron accelerator make a continuous treatment of fabrics incommercial facilities more practical from an economic standpoint.

In general, the durability of flame resistance of a cotton fabrictreated with triallyl phosphate and N-methylol acrylamide and thereafterirradiated with 2.0 megarads of ionizing radiation in accordance withthe invention is dependent on the amount of add-on and the ratio of thetriallyl phosphate to the N-methylol acrylamide comonomer. About 15.0percent add-on is about the lower limit of add-on when a ratio of 8.3parts of triallyl phosphate to 1.0 part by weight of N-methylolacrylamide is employed, in order to obtain good flame resistance whichis retained after 15 launderings. Within the add-on range of 1533percent, in order to obtain durability of flameresistance to laundering15 times, it is necessary to employ a ratio of trially phosphate toN-methylol acrylamide of at least about 2 to l by weight. A lower ratiomay produce initial flame resistance and varying degrees of retention ofsuch flame resistance after laundering, but lack of resistance to 15launderings. It is thus apparent that widely varying degrees of flameresistance and durability of flame resistance with respect to repeatedlaunderings are possible by varying the ratio of triallyl phosphate tocomonomer and varying the add-on of the solid polymer produced from thetriallyl phosphate and the selected comonomer.

In testing fabrics treated in accordance with this invention to impartflame resistance and laundering durability with respect to flameresistance thereto, the flame resistance test which has been employed isthe Vertical Bunsen test (Method 5903, Federal Specification CCC-T-191). The laundering method employed to determine durability of theflameproofness imparted to the fabrics to repeated launderings is Method5556 of Federal Specification CCC-T-191, which consists of a series ofsuds and rinse cycles using a detergent and sour. The highesttemperature during the wash cycles was 140 F.

Add-on is defined for the purposes of this invention as the diflerencebetween the final dried and conditioned weight of the treated materialand the initial dried and conditioned weight of the material beforetreatment thereof divided by the initial dried and conditioned weight ofthe material before treatment thereof, multiplied by 100 to convert topercentage. It generally describes the percentage increase in weight ofthe treated material due to the solid polymer formed in situ thereon asa result of the irradiation of the material impregnated with thephosphorus compound and the comonomer.

Having described in general terms the conditions under which the flameresistant material of the present invention is prepared, we will nowproceed to disclose specific examples of the production of flameresistant materials in accordance with the above-described principles.

It will be understood, of course, that the above-described principlesand other advantages of our invention may also be accomplished bysuitable variations of the detailed method steps, about to be set forthbelow, which are intended to be for illustrative purpoes, and not forthe purpose of limiting the scope of our invention.

EXAMPLE I A 9 x 12 in. sample of 8.2 oz. cotton sateen fabric wasimmersed in a solution containing 125 cc. of triallyl phosphate and 25cc. of N-methylol acrylamide (60% aqueous solution by weight). In thisproportion, 8.3 to 1 of triallyl phosphate to N-methylol acrylamide byweight, the two chemicals are miscible. The sample was squeezed to a wetpick-up of 100 to 125% by weight, placed in a sealed 4 mil. polyethylenebag and exposed to 2 megarads of irradiation in air at room temperatureusing a 24 mev., 18 kw. electron LINAC as the source of radiation,Electron irradiation consisted of scanning the sample with an electronbeam approximately 3-4 cm. in area as the sample moved through the beampath on a conveyor. The scan width was 16 in. and the dose rate, whilethe pulsed beam was on, was rads/sec. The repetition rate was 60pulses/sec. and the pulse duration was 5 micro-sec. The sample was heldin a vertical position during irradiation. The sample was then rinsed inhot water (40 C.) for 2 min. and dried at 100 C. in an oven. The add-onof dry solids on the fabric was percent by weight. Flame tests were madeusing the Vertical Bunsen test (Method 5903 of Federal Test Method Std.No. 191) both before and after laundering according to Method 5556 ofthe same Test Method Standard. Initially the after-flame was 0 sec. andthe char length was 5.8 in, After 15 launderings, the after-flame was 0sec. and the char length was 5.0 in.

EXAMPLE II The same type of fabric of the same sample size as in ExampleI was treated with the same ratio of chemicals as used in Example I andthen exposed to 4 megarads of irradiation in air at room temperatureusing a 1.25 10 Ci Co isotope source. Gamma irradiation was underambient conditions with a dose rate of 2.843.86 10 rads/min. After theradiation exposure, the sample was rinsed in hot water (40 C.) for 2minutes and dried at 100 C. in an oven. The add-on of dry solids on thefabric was 26 percent by weight. Flame tests initially were 0 sec.after-flame and 5.0 in. char length; after 15 launderings 2 sec.after-flame and 5.5 in. char length.

EXAMPLE III The same type of fabric of the same sample size as inExample I was immersed in a solution of 10 gms. of acrylamide, 10 cc. oftriallyl phosphate, 5 cc. of water and 10 cc. of methanol. The samplewas exposed in the same manner as in Example II, but to 6 megarads ofirradiation. After rinsing and drying as in Example I, the flameresistance of the treated fabric was 0 sec. afterfiame and 3.9 in. charlength.

EXAMPLE IV The same type of fabric of the same sample size as in ExampleI was immersed in a solution containing 10 cc. acrylonitrile by weightaqueous solution) 10 cc. of triallyl phosphate, 5 cc. of water and 5 cc.of methanol. The sample was exposed in the same manner as in Example II,but to 6 megarads of irradiation, After rinsing and drying, as inExample II, the flame resistance of the treated fabric was 0 sec.after-flame and 7.1 in. char length.

EXAMPLE V The same type of fabric of the same sample size as in ExampleI was immersed in a solution comprising 20 cc. of triallyl phosphate and20 c. of acrylic acid. The sample was exposed in the same manner as inExample II to 4 megarads of irradiation. After rinsing and drying as inExample II, the flame resistance of the treated fabric was 0 sec.after-flame and 4.6 in. char length.

EXAMPLE VI The treating solution containing triallyl phosphate andN-methylol acrylamide in a weight ratio of 4.8 to 1 contained in apolyethylene bag was subjected to 3 megarads of irradiation in the samemanner as Example I. The product was a water insoluble polymer which didnot propagate flame when exposed to and withdrawn from a Meeker burnerflame.

EXAMPLE VII The same type of fabric of the same sample size as inExample I was immersed in a solution of 15 cc. of dimethyl hydrogenphosphite and 15 cc. of n-methylol acrylamide (60% aqueous solution byweight). The sample was subjected to 4 megarads in the same manner as inExample II. The add-on of dry solids on the fabric was 18 percent byweight. After rinsing and drying as in Example I, the flame resistanceof the treated fabric was 0 sec. after-flame and 6.1 in. char length.

While the invention has been described above in terms of first treatinga material with a phosphorus compound, such as triallyl phosphate, and acomonomer, such as N-methylol acrylamide, followed by irradiating thematerial with ionizing radiation to produce a copolymer of thephosphorus compound and the comonomer in situ on the material, it willbe understood by those skilled in the art that the material may beirradiated with ionizing radiation first and thereafter treated with thephosphorus compound and the comonomer to produce a copolymer thereof onthe material. It is believed that the copolymerization of the phosphoruscompound and the comonomer within a short time is brought about due tothe presence of free radicals produced in the material by the ionizingradiation and that such free radicals may be produced either before orsubsequent to the treatment of the material with the phosphorus compoundand the comonomer with substantially equally effective results. It maybe desirable to exclude oxygen or to maintain the material at arelatively low temperature during and after irradiation if theirradiation is carried out prior to the application of the phosphoruscompound and the comonomer in order to retain a maximum number of freeradicals in the material for a given dose of irradiation until thereactants are applied thereto. Other methods known in the art forproducing free radicals in a material, such as the application of freeradical producing compounds, may also be used to treat the materialeither before or after application thereto of the phosphorus compoundand the comonomer to produce a copolymer having durable flame retardancycharacteristics in situ on the material.

One of the great advantages of the present invention resides in the factthat very good flame retardancy in cotton fabrics, as well as othernormally inflammable materials, can be obtained with relatively lowadd-on and without the application thereto of high temperatures. Furtherin this regard, the dosages of ionizing radiation required arerelatively low so that relatively slight degradation of the fabric orother material is caused by the treatment. But most importantly, theflame resistance imparted to the fabrics or other treated materials isvery durable with respect to standardized laundering procedures.

Although the tear strengths of fabrics treated in accordance with theinvention are somewhat less than those of the untreated fabrics, theyare still sufficiently high to make the fabrics fiame-proofed inaccordance with the present invention very useful whereverflameproofness is required in a fabric. This is especially true withrespect to many fabric uses by the Armed Forces since the elimination ofinflammability from clothing, shelter, and other normally inflammableitems is considered a primary objective and the durability offlameproofing treatments to repeated laundering is most important,especially in clothing items, for the maintenance of flameproofness ofsuch items without the necessity of retreatment during normal livesthereof.

We wish it to be understood that We do not desire to be limited to theexact details described for obvious modifications will occur to a personskilled in the art.

We claim:

1. A process for flameproofing an inflammable material comprisingimpregnating said material with a phosphorus compound selected from thegroup consisting of triallyl phosphate, diallyl phosphate, monoallylphosphate, and dimethyl hydrogen phosphite and a comonomer selected fromthe group consisting of N-methylol acrylamide, acrylamide, acrylic acid,and acrylonitrile and thereafter irradiating said impregnating materialwith a dose of ionizing radiation sufl'lcient to produce a copolymer ofsaid phosphorus compound and said comonomer on said material.

2. A process as set forth in claim 1, wherein the addon of saidcopolymer on said material is at least about 15 percent by weight.

3. A process as set forth in claim 1, 'wherein said phosphorus compoundis triallyl phosphate and said comonomer is N-methylol acrylamide andthe add-on of said copolymer on said material is from about 15 to about33 percent by weight.

4. A process as set forth in claim 3, wherein the ratio by weight ofsaid triallyl phosphate to said N-methylol acrylamide is at least about2 to l.

5. A process as set forth in claim 1, wherein said dose of ionizingradiation is from about 2 to about 25 megarads.

6. A flame resistant material having a copolymer of a phosphoruscompound selected from the group consisting of triallyl phosphate,diallyl phosphate, monoallyl phosphate and dimethyl hydrogen phosphiteand a comonomer selected from the group consisting of N-methylolacrylamide, acrylamide, acrylic acid, and acrylonitrile depositedsubstantially uniformly on said material.

7. A flame resistant material as set forth in claim 6, wherein theadd-on of said copolymer on said material is at least about 15 percentby weight.

8. A flame resistant material as set forth in claim 6, wherein saidphosphorus compound is triallyl phosphate and said comonomer isN-methylol acrylamide and the add-on of said copolymer on said materialis from about 15 to about 33 percent by weight.

9. A flame resistant material as set forth in claim 8, wherein the ratioby weight of said triallyl phosphate to said N-methylol acrylamide is atleast about 2 to 1.

10. A flame resistant material as set forth in claim 6, wherein saidcopolymer is formed on said material by exposure of said material to adose of ionizing radiation of from about 2 to about 25 megarads withsaid phosphorus compound and said comonomer absorbed on said material.

References Cited UNITED STATES PATENTS 2,660,543 11/1953 Walter et a1.117-136 2,714,100 7/1955 Fontoy et a1 117---161X 3,934,555 4/1960 OBrienet a1 1l7l36X 2,998,329 8/1961 SoVish et a1 117-9331 ALFRED L. LEAVITI,Primary Examiner K. P. GLYNN, Assistant Examiner US. Cl. X.R.

117-136, 161P, 161UN, 161UZ; 204-15922; 2528.1

